1 82 TRANSPIRATION AND ASCENT OV SAP ch, 



might be rendered permeable by exposure to low tem- 

 perature then suggested itself. At the same time, it was 

 apparent that the low temperature would have the advan- 

 tage of arresting changes taking place in the tissues experi- 

 mented upon. To this end the experimental tissues were 

 immersed in liquid air. Tissues thus treated immediately 

 become frozen hard. From the liquid air they were 

 without delay transferred to a stoppered vessel to prevent 

 the condensation of moisture on them from the atmos- 

 phere. When they had assumed the temperature of the 

 surroundings, they were pressed in the usual manner. 



Table 25. 

 Comparison of Saps Extracted by Various Methods. 



